Datapoint from trying to take an earlier flight from CDG as a Conc with my SO as Plat:

• Check-in supervisor very courteous, but as an outstation they could not access our original bookings (for the evening flight) so as to move us to the midday flight for which check-in was open when we showed up at the check-in desk. She mentioned they get this request repeatedly, but as they are not EI staff they are physically unable to access bookings for which check-in is not currently open. Advised to call and persist with call centre, who tend to eventually give in after reinforcing the point that it is impossible to do at CDG outstation.
• Ticket desk at CDG T1 of no help.
• Conc Egyptian call centre agreed to move only me to the earlier flight exclusively as part of the 'Conc' benefit (and ignoring my Advantage fare), but refused to move Plat SO as per her Advantage fare. 45mins of back and forth (including calling the Plat line simultaneously) with the call centre agents insisting that standby for Advantage ticket only possible at the airport.
• Finally call centre agent agreed to move SO after the 3rd time I handed the phone to the check-in supervisor at CDG, only for check-in to close 1h before the flight. Check-in supervisor very upset with agent, said she will be filing an operational report as agent refused to make the change on time, and the latter was now in the process of making changes after check-in was closed and this would delay the flight.
• Ultimately only my flight was moved up, my SO wasn't. Missed my newly-booked standby midday flight on purpose, supervisor told me not to bother calling the Conc line again to re-rebook, and reassured me I will be taken care of when check-in re-opens and she will personally reinstate to my original evening flight to travel together with SO.

Tldr: Do not put yourself through availing of 'standby for earlier flight' if travelling from CDG as a non-Concierge.